1. Field of the Invention
The present invention relates to a composition for forming a resist underlayer film, and a pattern-forming method.
2. Discussion of the Background
Substrates used for semiconductor devices have an intended pattern. A process for patterning the substrate includes, for example, the steps of: depositing a photosensitive substance, called a resist composition, on the substrate to provide a resist film; exposing a predetermined region of the resist film; developing the resist film and removing a light-exposed site or a light-unexposed site to obtain a predetermined resist pattern; dry etching the substrate by using the obtained resist pattern as an etching mask; and the like.
In such a patterning process, ultraviolet rays such as an ArF excimer laser beam are used as a source of exposure lights for exposing the resist film; however, demands for microfabrication of large scale integrated circuits (LSIs) are increasingly growing in these days, and a required resolution has reached a level of no higher than the wavelength of the exposure lights (ultraviolet rays). In the case of the required resolution being at a level of no higher than the wavelength of the exposure lights, as just described, an exposure process latitude such as an exposure dose latitude and a focus latitude tends to be insufficient. In order to compensate for such an insufficient exposure process latitude, it is effective to improve the resolution by decreasing the film thickness of the resist film; however, when the film thickness is decreased, it may become difficult to secure a resist film thickness necessary for etching the substrate.
Thus, a process including providing a resist underlayer film between a substrate and a resist film, once transferring a resist pattern to the underlayer film to form an underlayer film pattern, and thereafter transferring a pattern to the substrate by means of the underlayer film pattern as an etching mask has been investigated.
As a composition for providing the aforementioned resist underlayer film, a composition composed of a component that exhibits etching resistance is preferred, for example, a composition containing a polymer that has a high carbon content and includes an aromatic ring that absorbs energies during the etching, e.g., heat curable phenol novolak, a composition containing a polymer having an acenaphthylene skeleton, and the like have been proposed (see Japanese Unexamined Patent Application, Publication Nos. 2001-40293 and 2000-143937). In addition, a composition containing a copolymer of a styrene derivative or an allylbenzene derivative with a nortricyclene derivative, or the like has been also proposed (see Japanese Unexamined Patent Application, Publication No. 2008-65303).